The present invention relates to computer systems and more particularly to an apparatus for improving memory access times of a high speed peripheral device making accesses to memory.
It can be advantageous in the present state of the art for a computer system which uses, for example, a 16-bit data word to employ memory modules which operate with a 32-bit word. To most effectively use the capacity of such a memory, one 16-bit data word is stored in a first half of a 32-bit memory word, while a second data word is stored in the second half of the memory word. In order to perform a write of one data word to memory, the present contents of the relevant 32-bit memory word are first fetched from the memory storage elements. Then in registers, half the memory word is replaced with the data word to be written. Finally, the modified thirty-two bits are stored in the memory elements.
It has been conceived in accordance with the present invention that certain circumstances permit a considerable improvement in access times to a doubleword memory. In particular, where a high speed peripheral device such as a magnetic disc writes a series of words to sequential addresses in memory, it would be advantageous if each pair of 16-bit data words destined for a 32-bit memory word could be stored there in one write operation rather than two.